The invention relates to electronic devices, and in particular, to speed detection methods and devices.
An optical range finder calculates a distance by measuring the time during emitting a laser pulse at an object and receiving the reflected laser pulse. The pulse reaches the object and is reflected back to the range finder. The speed of a moving object can be determined by acquiring two distances thereof at different times and dividing distance difference by the time difference. FIG. 1 is an ideal schematic diagram of laser pulses reflected by a moving object for distance measurement. Assuming the object is measured 200 times, FIG. 1 shows only a portion of distance measurements thereof. The horizontal axis in FIG. 1 represents distance, and the vertical axis represents the orders of reflected laser pulses, i.e. the distance measurements. The orders of reflected pulses have fixed intervals. Each reflected signal corresponds to a distance derived by a distance formula. The speed of the object can be calculated utilizing the reflected pulses distributed in FIG. 1. Reflected pulses may comprise noise due to sunlight or other interference factors. Thus, the actual distribution of reflected signals received might be as shown in FIG. 2 (only a portion is shown). For getting the speed information from FIG. 2, it is necessary to filter the noise therefrom.
U.S. Pat. No. 6,466,307 B2 discloses a signal processing method and device for laser range-finder, wherein the distribution of actual reflected laser pulses directed at an object is stable when noise is randomly distributed, and the actual reflected pulses are accordingly retrieved statistically. A distance measurement by a conventional range finder, however, requires a certain period of time, such as 0.5 seconds, during which the moving object may continuously change locations, causing the distribution of actual reflected pulses to be unstable and thereby disadvantageous to reflected pulse extraction.
Additionally, speed measurement must also be acquired in a short time, such as 0.6 seconds, insufficient for two distance measurements by a typical range finder. Thus, a typical range finder has difficulty in acquiring two measured distances to determine speed.